Some engine systems may include devices such as throttle turbine generators to use energy from a pressure difference across a throttle that is otherwise wasted in an intake passage of an engine. In some examples, the throttle turbine generator includes a turbine mechanically coupled to a generator which may generate current that is supplied to a battery of the engine. By charging the battery with such a generator, fuel economy of the engine system may be improved, as compared to charging the battery with an engine driven generator.
The turbine driven generator may not supply enough current to maintain the battery charge under some conditions, however. As such, the engine system may include a turbine driven generator (e.g., a throttle turbine generator) and an engine driven generator. In such a configuration, fuel economy of the engine may decrease when the engine driven generator is used, thereby decreasing the overall efficiency of the engine system.
The inventors herein have recognized the above problem and have devised an approach to at least partially address it. Thus, a method for an engine is disclosed. In one example, the method comprises, when a state of charge of a battery is less than a threshold, directing intake air through a throttle bypass around a throttle disposed in an intake passage of the engine and through a turbine to drive an auxiliary generator. The method further comprises, charging the battery via the auxiliary generator.
In such an approach, the battery may be charged by the auxiliary generator when the state of charge of the battery is less than the threshold. The threshold may be a first, high threshold which corresponds to a maximum state of charge of the battery, for example. In some examples, a mechanically driven primary generator may be used to charge the battery in addition to the auxiliary generator only under some conditions, such as when the state of charge is less than a second, low threshold or when a vehicle in which the engine is positioned is decelerating. In this manner, charging of the battery is coordinated between the primary generator and the auxiliary generator such that charging of the battery via the primary generator is reduced. As such, fuel consumption due to use of the primary generator may be reduced.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.